Pyrometer



Feb. 28, 1928.

A. A. GRUBB PYROMETER Filed- Ag. e, 1925 lift YV Willi:

Patented Feb. 28, '1928.

UNITE STATE PArNr ADIN A. GRUBB, F MANSFIELD, OHIO, ASSIGNOR TO THE OHIOBRASS COMPANY, 0F

' MANSFIELD, GHIO, A CORPORATION OF NEW JERSEY.-

PYROMETER.

Application led August 6, 1925. Serial No. 48,481.

My invention relates to improvements in Jherum-electric pyrometers and`particularly .vhere they are intended for use with molten netal tomeasure'the temperature of the mol- :en mass at its interior.

One of the objects of my invention is to provide a thermo-electriccouple whereby the temperature of a liquid mass may be measured belowthe surface and not at the surface of the mass. Another object of myinvention is to protect both elements of the couple beyond their hotjunction from contact with the hot liquid.

l Another object of my invention is to protect the couple from thecorrosive actionl of `gases or liquids. Astill further object'of myinvention is to lminimize the temperature lag so that an accuratereading may be se-v cured as quickly as possible and before thetemperature to be measured -has had an opportunity of changing.

Another object of my invention is to provide a device in which themeasurement of temperature is taken at the extreme or hot end of theinstrument. A stillI further object of my invention is to provide aconstruction in which the junction of the couple is intimately subjectedto the heat of the mass, the temperature of which is to be measured.

A still further object is to provide a device in which the thermaljunction of the elements or the hot endis kept as close to the tip ofthe sheath as possible. A still further object of my invention is toprovide a sheath in which the mass at its tip adjacent the hot end ofthe couple is made as small as possible.

Other objects will be'disclosed to and recognizediby those skilled inthe art as .I further describe my invention which resides in the' newand novel construction. combination and relation of the various partshereinafter fully described' anddisclosed in the' accompanying drawing.

Inthe drawing:

Fig. 1 shows my invention and the method of application in measuring thetemperature of a pot of molten metal which is shown in section.

Fig. 2 is an enlargement-of the hot end Fig. 6 represents the hot end ofa semiprotected couple with which the trade is now familiar in which oneelement of the couple is the outer tube closed at one end and the otherelement constitutes a wire eX- tending through the tube and having itsend embedded in the closed end of the tube.

Fig. 7 represents the hot end of a tected couple.

Figs. 8, 9 and 10 are modified tips from that shown in Fig. 2.

I have found in my experience with the use of and experiment withvarious. pyrometers for measuring the temperatures of mol' ten metalthat the open couple shown in Fig. or the open end couple in which theelements are not/joined at A and which are the simplest and cheapestforms in which the elements may be used are far from satis'-y factorywith which to secure accurate temperature readings of the metal. It isdesirable and highly important in measuring the temperature of moltenmetals that the temproperature be'secured as quickly as possible at thetime desired and that the temperature be secured at the center or theinterior portion of the'mass. for I find7 contrary to the usual belief,that the mass of metal is not ofthe same temperature throughout and thatthe temperature of the surface is' more than likely to be considerablylower than that of the metal within the mass, and, therefore, it is veryimportant to have a pyrometer by means of which the temperature at thecenter or interior of the molten mass may be secured quickly and'not thetemperature at the surface.

As is well known' the thermo-electric couple, generally speaking,measures the diierthe couple whichis called the hot end and the oppositeend of the couple which is called the cold end, therefore, in the opencouple shown in Fig. 5 the hot end or`junct1on is at A. If sucha coupleis inserted in a pot of molten metal to the'.V line b-b such but'it willbe the difference between the tem` parat-ure coinciding with points onthe line b-f and the cold end of the couple. In

other words, the hot7 junction has been moved from A to the surface b-bof the metal due to the exposed elements being. short circuited -by themetal and. the temperature which the open couple will measure will bethe difference between that of the surface of the metal and the cold endof the couple and not the difference between that of the interior andthe cold end.

Another difficulty with the unprotected couple is that the element-s areusually quite small and hot metal tends to corrode the same quiterapidly and if they are large, the corrosion increases and becomes aheat 1nsulator thus affecting theetliciency and ac.

cepting at their junction A, and to secureA a reading at the interior ofthe mass of metal, but such coatings are very unsatisfactory as they arebrittle and ver short lived and do not overcome the unreliability ofthe' readings.

Where the semi-protected couple, ,as represented in Fig; 6, is employed,I find that there isa considerable time lag in securing the properreading, of the metal due largely to the outer element orl enclosingtube having a considerable mass 'and requiring con-l siderable time tobring the same up to vthe temperature of the molten metal and this timeis Voften sufficient to permit the .mass of meta-l to have changed itstemperature considerably. This mass, however, can be reduced and thetime-lagof the instrument reduced, `but again, this form of couple hasits end immersed in the molten metal up toa point corresponding with theline c-c and, therefore, the temperature measured is Y not thedifference' between that of the junction B and that of the coldl end ofthe couple, but takes into account the temperature at the surface of themetal which is colder than the metal at the point B and whlch contactswith one element on the line c-0,'and' when the instrument is used tomeasure the temperature of a molten copper- 4 alloy,` the alloy .formsa'conducting path 1n parallel with the tube between the lpoints B andci-o and this may affect the reliability of the readings due to changingthe electrical characteristics of the coup-le at the hot end.Also,'since the easing forms one element of the couple, it is subject tooxidi'zation and corrosion and becomes coated with slag` which altersthe thermal characteristics of thecouple andv reduces the reliability ofthe readings. But, I find the semi-protected type superior to theprotected form in some respects, while the protected form is superior tothe semi-protected form in other re-l spects.

Fig. 7 shows the hot`end of a protected couple in which the couple isenclosed in a casing such as iron, porcelain, etc., but the couple 1snot connected to or 1n contact wlth the casing, therefore. the heatwhich the convectionor radiation or both. If the cou-- ple shouldContact with the sheath it is usuaily 'a mere point of contact in whichthe extreme end of the connected couple accidentally engages theYcasing. This form of couple is very slow and not applicable to thetaking of quick readings as its time lag is great and it is alsoinaccurate asthe end of the couple may, at times, make contact with thesides or end of the casing.

'In order to overcome'as far as possible the defects which I found inthe forms represented in Figs. 5, 6 and47 I conducted a series `ofexperiments which resulted in the form of pyrometer shown in Figs. 1 and2 and which I find a reatimprovement over either-of the forms sown inFigs. 5. 6 and 7.

In, the preferred embodiment of my invention I employ a tube 1 which ispreferably ofimetal and may be of iron and on the upper end of this tubeis positioned a handle 2 of wood or other insulating material which maybe round or square or of other shape and which is held in position onthe tube 1 by means of a screw 3. The upper halfof the wood handle 2 hasone portion '4 detachable. The portion 4 and its correspondingr por-tion5 is hollowed out in order to permit the oppositely disposed contactmembers 6 to be secured therein. The contact members 6 each compriseaplate of copper or brass which is secured to the wood portion 5 by meansof the screws 7 and 7. The contact strips 6 are, shown as spaced andinsulated from each other. The part 4f,v which might be termed thehandle cover, is provided with a metal plate 8 secured thereto andprovided with projecting dowels 9 which engage the 'recess 10 in themember 5 1n orderv to hold llt lll

the two parts against side movement and to further hold the `member 4 inposition with respect to the member 5 a screw is inserted through theorifice 11 and extending into the orifice 12 on the member 5 therebyreventing removal of the member 4. Projecting from the upper end of thehandle 2 are insulated lead wires 13 and 14 which connect to the contactplates G and to the indicatlng instrument `15 which is usually of amillivoltmeter type calibrated in degrees of temperature in place ot'the milli-volts. The lead wires 13 and 1-1 are covered with a protectinginsulation 1G and at the pointA they enter t'he handle 2 are protectedby means of a helically wound spring 17 which prevents the wires beingbent short and therefore decreasing their life. The leads 13 and 14 maybe of the same metal as the thermocouple elements or they may be ofcopper or other metal, but the former is preferred and these lead wiresare secured to the contact strips 6 by means of the screws 7 which alsofunction to secure the wood strips to the member 5.

The thermocouple proper comprises the two elements 18 and 19 and. as iswell known, these are of different metals such as platinum-rhodium orchroniel-alumel or other dissimilar metals which will give the desiredresults. The wires forming the couple are positioned within theprotecting tube 1 and have 011e of their ends joined as by twisting orwelding. which I call a thermal union. and their other ends secured eachto one of the contacts 6 by means of the screws 7. It is necessary tomaintainthe elements 18 .and 19 electrically separated and insulatedfrom each other and from the tube 1. therefore. I position upon theelements 18 and 19 a refractory insulating element 20, which may be ofalundum, clay, porcelain, asbestos or other suitable material and lshownin section in Fig. 4. These insulating members 20 I have shown as inshort lengths as it is easier to manufacture them in short lengths,although they may be, formed. into a single insulatingelement andemployed with equal efficiency or the insulating element 20 nia-v beiliade of a plastic material applied within the-tube and about theelements 18 and 19 and then hardened. 1

In order to protect the thermocouple elements 18 and 19 from contactvwith the molten metal 21 I employ a protecting sheath which may be ofany sui-table material to meet the requirements. This is preferably (itlmade Ofmetal, but it may be made 0f quartz or other refractory materialswhich will`v After considerwithstand the conditions. able experimentingwith metals lof diti'erent composition I have found that when the coupleis used with alloy metals such as of copper. zinc, etc.. that somecompositions will dissolve and others cori-ode or oxidizev badly. but Ihave found that a sheath 1nade ol iron having a high content ofchromium, (20% to 30% approximately), is susceptible to the least amountofcorrosion and dissolution and is satisfactory for general foundry workand will give very satisfactory results when used with copper or copperalloys.

To protect the elements 18 and 1.9 from contacting with the sheath 22and to insulate them from each other and from the sheath I employ asingle tube 23 of alundum, quartz or other suitable materialv andprovide therein two spacmlholesl to receive the elements 18 and 19 and asection ot' which tube is shown in Fig. 3. The sheath is held inposition within the protecting tube 1 b v means otl the screws 2i whichpass through the'boss which may be welded on the tube 1.

The sheath 22. it will be noted. comprises a shell 2G the outer face ofwhich is tapered and the recess 27 therein has straight or parallelwalls. The lower end of the sheath is contracted and provided with apassage 28 vthe elements to the extreme end of the sheath. as at C. orby compressing or squeezing the walls otl the portion 30 into contactwith the thermocouple elements. as in Figs. 8 and 9. thereby forming athermal union between the elements 18. 19 and the tip 30 whichelectrically connects the elements together or adds to the connectionmade by twisting or welding. etc.

It will be noted that the walls of the sheath at the lower end thereofare very thin as compared with the walls at the upper end and this isvery important as it reduces to a minimum the time lag in securingreadings of the molten metal as there is very little mass for the moltenmetal to heat up at the hot end of the elements.

The sheath 22protects both elements of the couple from contact with themolten material and hence their cliaracteristics are not changed oraffected by the hot molten material and` therefore. the readings aredependable as compared with those ot' other types known to applicant anddescribed above.

The intimate thermal union formed bctween the elements ot' the coupleand theI member 30 either by compression, peening or welding. etc..assures that the thermoelectric junction X of the two elements, which isthe point of contact of the two .clements nearest the indicator 15 andwhich point islat the portion 30,` will be subjected to Thetwisted. orun-v and influenced by the heat of the material to be tested and can hesubmerged to that point below -the surface of the molten materialdesired by the operator and that the heat will be transmitted to thethermo-electric junction X in the shortest time and most efficientmanner and with the least errors as the temperature at the surface ofthe molten mass will not affect the readings.

In Fig. 8 I have shown the hot ends of the couple elements as twistedtogether, inserted into or projecting throilgh the opening 28 in theportion 30 and then the Walls of the portion 30 are squeezed or peenedintoA intimate mechanical contact with the elements 18 and 19 forming athermal union therebetween. This insures the heat, the

temperature of which' is to be measured'being conducted to .thethermo-electric junction of the elements with very little timelag. Thewalls of the member 30, as in the case of the walls of the member 30 inFig. 2 are made relatively thin to reduce the mass as much as practicaland permit the heat to travel to the thermo-electric junction X of theelements las quickly as possible hence bringing the temperature of thejunc- 4-tion of the elements up to that of the hoti7 v metal in theshortest period of time.

. In Fig. 9 is shown a modification in which the hole 28 does not extendentirly through a the. portion 30, butthe elements are brought intoyintimate mechanical contact with the -portion 30 by peening orcompressing the walls 'of the member 30 into close engagement with theelements' 18 `and 19 or if the melting point ofgthe elements 18 and 19are suiiciently low as compared with that of the sheath, then the sheathmaybe heated to the melting point of the elements 18 and 19 and so fusedto. the walls of the hole 28.

It will be seen that the elements `18 and 19 and the 'sheath canbe'quickly renewed and replaced .by loosening the screws 7 and 24 andthis is an'advantage when usingA the .instrument to measurethetemperature of molten metall as thensheath 26 is sometlmes attackedbythe metal after a time. The elements 18 and19 may be welded to theportion 30 by projecting the elements through the hole 28 and thenapplying an electric arc A or Oxy-acetylene a'me to the exposed ends andmelting them down and into a fused union with the end 30l of the sheath.v

B y my invention I have protected both elements and the lthermo-electricjunction A X from contact -with themolten metal or other material, thetemperature of which is to be measured, by the use ofv a'sheath, and Ihave provided means torkeep the elements out of contact with each otherland with-the sheath excepting at the' thermosmall as practical and Ihave made the conto a high degree of accuracy measure the f temperatureof a molten mass at any interior point.

The portion of the elements projecting below the end face of the tip 30will contact directl with the material to be measured and will form,when new, a thermal union between the couple and the material measured,but this union will decrease in efficiency if the couple is used tomeasure the temperature Vof molten metal or corrosive materials and Willsluf olf, therefore, I do not depend upon the thermal union of theelement direct with the material measured, but bring the thermo-electricjunction X as close to the end of the tip 30 as possible and make theconnection between the couple and the tip .as perfect as possible andthe' tip as small as praeticah In the modification in'Fig. 10 theelements 18 and 19 are not directly connected as by twisting,` welding,l etc., but are each provided with its own passage through the tip '30which may be squeezed into intimate con- `tact with the v' elements orthe outer ends may be welded tothe outer face of the tip 30 or both., Inthis easel-,the `thernlo-electric vjunction is at Xu and the interveningportion of the tip B0 formsa part ofthe june. tion, but as it is smallit does not affect the efficiency or the'rapidity of the couple.

There Will, of course, be other modifica-l tions which will suggestthemselves to those skilled inthe art and which will fall within thescope of my invention, the materials for instance may differ from thosegiven and the detailed construction, therefore, I do not wish to belimited other than by my' claims.

lI claim: c y 1. The combination -with a thermo-electric couple lvofdissimilar metalsl electrically connected together at one end to form athermoelectric junction therebetween of a sheath surrounding theelements and secured thereto at thermo-electric junction.

2. 4The combination with athermo-electric couple of dissimilar metalsmechanically sei cured together at one end to form a thermoelectricjunction therebetween of a sheath surroundin the elements and secured tothe couple-.at tie thermo-electric junction and forming a thermal unionwith the elements.

3. The combination of a thermo-electricl couple of'two dissimilarelements connected together to form a thermo-electric'junctiontherebetween, a sheath to protect the thermoelectric junction fromcontact with thema'- terial the temperature of which is to be lll() laoand to conduct measured and means comprising a portion of the sheathreduced to a very thin section and surrounding and engaging the elementsat the junction. to eieiently conduct the heat ot' the material. to thethernio-electric junction.

4. The combination With a thermo-electric couple ot' two dissimilarelements connected together tor a short distance at one end to form athermo-electric junction at one end of said connected portion, of meanssecured lo and enclosing the connected portion of the elements toprotect the junction and both elements from contact with the metal theheat of the metal to the junction.

5. A theru'lo-electric couple having a theri'no-electric junction andprovided with means to protect the couple and the thermoelectric junclion from contact With a mass of molten metal when the junction andcouple are plunged into and below the surface of the metaliand meanssecured vto the elcinents at the junction to conduct the heat ot' themetal lo the junction.

A thermo-couple comprising` a pair of elements ot' dissimilar metalhaving one end ot each clement united to form a thermoelectric junction,a sheath to protect the elements and the thermo-electric junction andhaving'means at its tip to receive the Said ends of the elements infused relation to the tip of the sheath,

7. A protecting sheath for a thermo-couple con'lprising an elongatedtubular member having an orilice' therethrough of two diil'ercntdiameters to receive the couple, the length ot' the orifice ot' largerdiameter being greater than that ot' the smaller diameter and theoutside diam-eter of the Wall of the greater diameter orilce beinggreater than the'outside diameter of the wall ot' the smaller diameterorilice, the wall of the larger diameter portion tapering to a thinsection adjacent the smaller .diameter portion and the in,

ner surface of the wall of the greater orifice adjacent the smallerorifice tapering to meet the inner surface of the Wall of the smalleroriiice.

S. A protecting sheath for the hot end of a thermo-couple comprising anelongated member having an orifice therethrough of two diameters toreceive the couple, the length of the orifice of the large diameterbeing greater than that of the smaller diameter and the lwall of thelarger diameter orifice tapering to a thin section adjacent the hot endof the couple, a reduced portion projecting from the above portion ofthe sheath and through which passes the reduced orifice, the wall ofthereduced portion being of as thin a section as practica] to avoid mass.

9. A protecting shath for a thermo-couple comprising a tubular portionhaving an orilice therethrough to receive the thermo elcments in spacedand insulated relation and having means at one end to cooperate withmeans on a support to secure the sheath to the support, a portionprojecting from the first said tubular portion and having a passagetherein to receive and securely engage the ends of the thermo elements1and grip the same to conduct outside heat direct to the thermo-electricjunction ot' the thermocouple. j

1l). A protecting sheath for a thermo-couple comprisingr an elongatedportion having an orifice tlwretlnrough to receive the elcments oi athern'io-eouplein spaced and insulated relation to eachother and to thesheath, a portion projecting Yl'rom one end ol" the elongated portion ofreduced diameter and provided with n'ieans to receive and grip the endsot the thermo elements" at their thermo-electric junction and adapted togrip j ymeans to engage the two elements and electrically connecttogether one end of each clement to form at theconnection of theelements and said means a thermo-electric junction therebetween and toprotect said junction from contact-with the material to bev tested.

12. The combination with a pair of dissimilar elements to form athermo-couple of means to Aengage and to mechanically and electricallysecure together one end of each element to form a thermo-electricjunction therebetween, to protect the junctionfrom contact with thematerialto be tested and to conduct heat directly to the thermo-electricjunction.

13. The combination With a thermo-electric couple of dissimilar metalshaving a thermo-electricv junction of a` sheath to protect the elementsand the thermo-electric junction and, having means compressed into closemechanical engagement with the end of the couple adjacent the junction.

14. The combination with a thermo-elec tric couple of dissimilar metalshaving a thermo-.electric junction of a sheath to protect the elementsand the thermo-electricV junction, the sheath having a materiallyreduced cross-section compressed into close mechanical engagement withthe couple at the junction. i

15. The combination with a thermo-couple of twov dissimilar elements.connected to gether to form a thermo-electric junction of very thinmetallic means securely engaging the elements at the junction to conductheat directly to the junction and protect the junction'and the elementsfrom contact with. the material, the temperature of which is to bemeasured.

:16. A thermo-'couple comprising a; pair of Ilm elements of dissimilarmetals and having the elements united for a short distance of theirlength at one end and providing a thermoelectric junction at the innerendof the connected portion intermediate the ends of the elements andmeans enclosing and protecting the thermo-electric junction and engagingthe elements at the thermo-electric junction to conduct-heat directly tothe thermoelectric junction.

17. A .thermo-couple comprising in combination therewith a sheath toprotect both elements of the couple from external iniuences tending toaffect the accuracy and reliability of the couple when in use andintimately connected with the elements to electrically connect theelements together to\ form Within the interior of the sheath and at saidintimate connection a thermo-electric junction and to quickly andaccurately transmit external heat to the thermo-electric junction.

tric couple of'two dissimilar metals securedl together at one end anddiverging from contacting with each other to form a thermoelectricjunction therebetween of a sheath surrounding the elements andcompressed into .engagement with the elements at the thermo-electricjunction and forming ay therlmal union with the elements at thethermoelectri'c junction and means to maintain'f'the elements beyond thethermo-electric junction electrically Separated and out of contact withthe Sheath. v

In testimony whereof I afl-lx my signature. ADIN A. GRUBB.

